Candles have been used throughout human history in numerous applications. These include lighting, heating, and providing decorative effects. In modem times, candles have been used primarily for their decorative effects as their lighting and heating abilities have been replaced by safer and more efficient heating and lighting systems.
In the broadest sense, candles comprise a flammable wick surrounded by a fuel source, typically a wax body. Upon lighting the wick, a portion of the wax adjacent to the flame becomes molten and is drawn upward into the wick, whereby fueling continued burning. As the candle continues to burn, the wick and fuel are slowly consumed until the candle is extinguished.
Candle making is an extremely mature art which has relied upon myriad variations, both new and old, to enhance the decorative effect of candles. For example, candles have been provided with fragrances, they have been molded into various shapes, they have been provided with multiple wicks, and they have been made in substantially the entire visible spectrum of colors. Additionally, candles may be of the conventional variety in which a portion of wax contained in a molten pool near the flame is allowed to drip along the length of the candle body, or, through the use of additives, candles can be made to be dripless.
Despite the numerous variations in the candle art, to date, candles capable of undergoing a reversible color change are not known to the art. While candles having concentric wax layers of different colors are known to provide multi-color effects when burned, none of the candles known to the art exhibit reversible thermochromic color changes. As used herein, the term "thermochromic" refers to the ability to change color based upon temperature.